The microbiome–cancer axis as a hidden contributor to early-onset tumorigenesis

The global incidence of early-onset cancer has surged by nearly 80% over the past three decades, yet the underlying causes remain poorly understood. While genetics and lifestyle are among the traditional risk factors, emerging evidence implicates the human microbiome as a potent and overlooked contributor to early tumorigenesis. Increases in the studies that are exploring the tissue-specific microbiome signatures such as the enrichment of Actinomyces and Bacteroidia in early-onset colorectal cancer, or Enterobacter and Neisseria in pancreatic tumors offer compelling evidence for age-stratified microbial contributions. Additionally, the recent works on the establishment of gut–testis, oral–gut, and gut–liver microbial axes are being explored to understand the modulation of systemic immune and endocrine landscapes in younger individuals that might unravel their unique predisposition to malignancy. Further, the microbiome–cancer axis has been regarded as a hidden driver in the initiation and progression of early-onset malignancies across diverse tissue types. Understanding this link will provide the missing mechanistic insights showcasing how microbial dysbiosis, biofilm formation, and microbially derived metabolites promote oncogenic inflammation, DNA damage, and immune evasion contributing to early-onset cancers. Considering the potential of these studies, microbial biomarkers with diagnostic promises that include probiotics, fecal microbiota transplantation, and diet have also been explored as emerging tools for prevention and therapy. Through this study, we aim to understand early-onset cancer through a patient microbiota and underscore an urgent need to integrate microbial dynamics into cancer surveillance and intervention strategies, especially for young and largely asymptomatic populations.